APOD: Hong Kong Sky (2010 Feb 06)

APOD Robot · Post by **APOD Robot** » Sat Feb 06, 2010 4:54 am

Hong Kong Sky

Explanation: This remarkable scene combines multiple exposures recorded on the evening of January 18th from a waterside perspective in Hong Kong, China. It follows a young crescent Moon, with brilliant planet Jupiter to its left, as they set together in the western sky. Their two luminous trails are faintly paralleled by trails of background stars. But easier to pick out are the short, bright airplane trails converging toward the horizon and the Hong Kong International Airport that seem to offer a frenzied imitation of the celestial tracks. Of course, the reflection of city lights and boat traffic follows the water's surface. Streaking car lights define the span of the cable-stayed Ting Kau bridge.

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al dumont · Post by **al dumont** » Sat Feb 06, 2010 5:37 am

being an amatuer I will simply say that I believe the photo is looking east at a rising moon and planet.

Case · Post by **Case** » Sat Feb 06, 2010 6:17 am

On January 18 2010, the moon rises and sets later than the sun. (Hong Kong local times: Sunrise: 07:06, Moonrise: 08:44, Sunset: 18:02, Moonset: 20:35) Thus, to see the moon in a dark sky, you have to look west after sunset.
Jupiter being on the left side of the moon is another clue for the western horizon.

soupphysics · Post by **soupphysics** » Sat Feb 06, 2010 9:15 am

I don't like it that much. It's messy and there isn't really anything fascinating in it.

geckzilla · Post by **geckzilla** » Sat Feb 06, 2010 11:46 am

Such is city life, soup.

neufer · Post by **neufer** » Sat Feb 06, 2010 1:39 pm

Case wrote:On January 18 2010, the moon rises and sets later than the sun. (Hong Kong local times: Sunrise: 07:06, Moonrise: 08:44, Sunset: 18:02, Moonset: 20:35) Thus, to see the moon in a dark sky, you have to look west after sunset.
Jupiter being on the left side of the moon is another clue for the western horizon.

Besides which, Hong Kong International Airport is WSW of the Ting Kau bridge.

neufer · Post by **neufer** » Sat Feb 06, 2010 4:12 pm

http://www.tsingma.com.hk/Web_pages/Intro_tmca/ting_kau_bridge_e.htm wrote:

<<The 1,177m long Ting Kau Bridge and the 500m long dual Approach Viaduct form a vital link in Hong Kong's new Route 3, connecting Hong Kong Island, Kowloon and the new airport at Chek Lap Kok to the New Territories and the mainland. Two main ramps connect to the Tuen Mun Highway and the Western New Territories.

The outstanding features of this unique cable stayed bridge are the 3 towers with heights of 170m, 194m, and 158m, located on the Ting Kau headland, on a reclaimed island in Rambler Channel and on the north-west Tsing Yi shoreline respectively. The arrangement of separate decks on both sides of the 3 towers contributes to the slender appearance of the bridge while acting favourably under heavy wind and typhoon loads. Each deck carries 3 traffic lanes and a hard shoulder. Spanning the 900m wide Rambler Channel, the Ting Kau Bridge ranks amongst one of the longest cable stayed bridges in the world.>>

antn_e · Post by **antn_e** » Sat Feb 06, 2010 9:50 pm

Surely planes have the white lights at the front, so the trails must be taking off and diverging not converging (unless they were flying backwards!)

neufer · Post by **neufer** » Sat Feb 06, 2010 11:12 pm

antn_e wrote:Surely planes have the white lights at the front, so the trails must be taking off and diverging not converging (unless they were flying backwards!)

The planes themselves are taking off and diverging
but they are leaving behind trails which converge back toward the horizon.
(And don't call me Shirley.

)
http://www.youtube.com/watch?v=lqrllkAO1uA

statman · Post by **statman** » Tue Feb 09, 2010 12:44 pm

Why aren't the Jupiter and Moon paths parallel as the "movement" is nearly all due to the earth's motion?

neufer · Post by **neufer** » Tue Feb 09, 2010 1:12 pm

statman wrote:Why aren't the Jupiter and Moon paths parallel as the "movement" is nearly all due to the earth's motion?

Only straight lines can be parallel.

These paths can only be straight lines if they are exactly on the celestial equator.

See: http://apod.nasa.gov/apod/ap090314.html
--------------------------------------------------------
1) A simple lens or pinhole camera produces a gnomonic map projection of the celestial sphere.

2) The gnomonic map projection displays all great circles as straight lines.

3) Right ascension lines and the celestial equator are great circles
. and, therefore, always appear as straight lines a gnomonic map projection:

4) All other celestial declination lines are curved in a gnomonic map projection
--------------------------------------------------------

statman · Post by **statman** » Tue Feb 09, 2010 4:07 pm

I meant - why are the paths not parallel - as in, the same apparent distance apart on the image: meaure with a ruler and you will see they are different distances apart between top annd bottom.

neufer · Post by **neufer** » Tue Feb 09, 2010 5:32 pm

statman wrote:I meant - why are the paths not parallel - as in, the same apparent distance apart on the image: measure with a ruler and you will see they are different distances apart between top and bottom.

http://apod.nasa.gov/apod/ap090314.html
Measure with a ruler and you will see these paths
are different distances apart between bottom & top.

The circular path of Ursa Minor around Polaris
is NOT parallel to anything because it is not a straight line.

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APOD: Hong Kong Sky (2010 Feb 06)

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